(a) Field of the Invention
The present invention relates to a mesoporous platinum electrode and a method for detecting a biochemical substrate using it, and more particularly to a mesoporous platinum electrode including an electrode with a mesoporous platinum layer covering a surface thereof, and a method for quantify the concentration of -glucose by detecting a selective response to the glucose oxidation reaction using the mesoporous platinum electrode.
(b) Description of the Related Art
A biosensor, in combination with electric devices, converts chemical information in a biological sample into an electrical signal, which can be easily treated. Biosensors are widely developed and applied in the medical field, due to the advantages of real-time selective monitoring of quantitative information of an analyte without complicated chemical and biological pre-treatments.
The study of biosensors for glucose has been extensively carried out for the purpose of glucose concentration monitoring for diabetes. The biosensor for glucose detection measures the concentration of glucose (analyte) using the enzyme layer that is immobilized in the confined region, generally on an electrode. Enzymatic glucose biosensors using enzyme have been studied extensively and developed in various types. However, there has been limited application because of enzyme instability. The temperature and pH affect severely on the activity of enzyme.
The studies on non-enzymatic biosensors for glucose detection have been carried out (Vassilyev, Y. B., Khazova, O. A., Nikolaeva, N. N. J. Electroanal. Chem. 1985, 196, 105; Beden, B., Largeaud, F., Kokoh, K. B., Lamy, C. Anal. Chem. 1996, 41, 701; Bae, I. T., Yeager, E., Xing, X., Liu, C. C. J. Electroanal. Chem. 1991, 309, 131; Sakamoto, M., Takamura, K. Bioelectrochem. Bioener. 1982, 9, 571; Kokkinidis, G., Xonoglou, N. Bioelectrochem. Bioener. 1985, 14, 375; Wittstock, G., Strubing, A., Szargan, R., Werner, G. J. Electroanal. Chem. 1998, 444, 61-73; Zhang, X., Chan, K.-Y., You, J.-K., Lin, Z.-G., Tseung, A. C. C. J. Electroanal. Chem. 1997, 430, 147-153; Sun, Y., Buck, H., Mallouk, T. E. Anal. Chem. 2001, 73, 1599-1604; Shoji, E., Freund, M. S. 2001, 123, 3383-3384). However, most of the non-enzymatic glucose sensors studied undergo interference by ascorbic acid (AA), uric acid, and 4-acetamidophenol (AP), which are important interfering species.
An example of a non-enzymatic glucose biosensor is one that utilizes the direct oxidation of glucose on a platinum surface (Anal. Chem. 2001, 73, 1599-1604). In the direct oxidation on the platinum electrode, the oxidation rate of glucose is much lower than that of interfering species, so it is very difficult to construct a non-enzymatic amperometric sensor using platinum on an electrode.
A possible method to alleviate the problems met by platinum is to use a Pt-Pb alloy electrode (Pt2Pb electrodes). Compared with pure platinum surfaces, glucose is electrochemically oxidized on Pt2Pb surfaces at remarkably negative potentials, and Pt2Pb is relatively insensitive to interfering species such as L-ascorbic acid (AA), uric acid, 4-acetamidophenol (AP), and so on. Moreover, Pt2Pb operates more stably due to insoluble Pb and larger responses than pure Pt. However, in spite of these valuable advantages, surface poisoning by chloride ions remains a serious problem, in which the amperometric signal diminishes rapidly in the presence of 0.01 N NaCl and eventually almost disappears.
The modification of platinum surfaces with other materials has also been attempted. Even though platinum surfaces modified by Tl, Pb, Bi, or WO3 reportedly show catalytic activity for glucose oxidation, the dissolution of metal ions and the toxicity of the heavy metal elements involved prevent these methods from being put to practical use.
Mesoporous materials have a pore size between 2 and 50 nm, and a micell structure or a liquid crystal structure consisting of surfactants induces the pore structure of the mesoporous materials. The surfactants consist of a hydrophilic head group and a hydrophobic tail group, and various self-assembled micell and liquid crystal structures are comprised of the surfactants in aqueous solution. Organic/inorganic nanocomposites are formed by interaction between the hydrophilic group of the surface of the micell or liquid crystal structure and the inorganic material, and mesoporous materials are obtained by extraction of surfactants. Mesoporous platinum was fabricated by this principle, and studies on characteristics thereof have been performed (e.g. Gollas, B., Elliott, J. M., Bartlett, P. N. Electrochimica Acta 2000, 45, 3711-3724; Attard, G. S., Glyde, J. C., Goeltner, C. G. Nature 1995, 378, 366-368; Attard, G. S., Goeltner, C. G., Corker, J. M., Henke, S., Templer, R. H. Angew. Chem. Int. Ed. 1997, 36, 1315; Whitehead, A. H., Elliott, J. M., Owen, J. R., Attard, G. S. Chem. Commun. 1999, 331-332; Attard, G. S., Edgar, M., Goeltner, C. G. Acta Mater. 1998, 46, 751-758; Birkin, P. R., Elliott, J. M., Watson, Y. E. Chem. Commun. 2000, 1693-1694; Elliott, J. M., Owen, J. R. Phys. Chem. Chem. Phys. 2000, 2, 5653-5659). Mesoporous platinum film was initially produced by electrodeposition from a hexagonal (H1) liquid crystalline phase composed of the non-ionic surfactant (octaethylene glycol monohexadecyl ether, C16EO8) (e.g. Attard, G. S., Bartlett, P. N., Coleman, N. R. B., Elliott, J. M., Owen, J. R., Wang, J. H. Science 1997, 278, 838-840). Reportedly, the electrodeposited platinum film with cylindrical hexagonally arrayed pores (pore diameter, 2.5 nm; pore-pore distance, 5.0 nm) was adherent and shiny. According to Evans et al. (Evans, S. A. G., Elliott, J. M., Andrews, L. M., Bartlett, P. N., Doyle, P. J., Denuault, G. Anal. Chem. 2002, 74, 1322-1326), mesoporous Pt films (Elliott, J. M., Birkin, P. R., Bartlett, P. N., Attard, G. S. Langmuir 1999, 15, 7411-7415) electrodeposited onto microelectrodes showed tremendous improvements in hydrogen peroxide detection sensitivity compared with bare platinum.